Alpha-methylene-gamma-butyrolactone and methyl alpha-methylene-gamma-butyrolactone are useful monomers in the preparation of both homopolymers and copolymers. In addition, the alpha-methylene-gamma-butyrolactone group is an important structural feature of many sesquiterpenes of biological importance.
U.S. Pat. No. 6,232,474 B1 describes a method for converting certain starting lactones to alpha-methylenelactones using a homogeneous or heterogeneous so-called basic catalyst that can be selected from the metal oxides, hydroxides, carbonates and phosphates, any of which may be supported or unsupported. The preferred reaction is the conversion of gamma-butyrolactone to alpha-methylene-gamma-butyrolactone. The basic catalyst may include additives and promoters to enhance catalyst efficiency. The method involves a reaction between the starting lactone and formaldehyde and may be carried out in a batch mode, optionally using an organic solvent and a phase transfer agent. The method is carried out at a temperature of at least 70° C. and a pressure less than or equal to 2000 psi (13.7 MPa). A problem inherent in the method is that the homogeneous catalysts must be used at high concentration to achieve good yields, but are not easily recycled. On the other hand, the heterogeneous catalysts, while more easily recoverable, do not provide as high conversion and selectivity.
It would be advantageous, therefore, to have a lactone conversion process that not only provides high conversion and selectivity, but also allows for easy catalyst recovery.